Asymmetrically-shaped combustion chamber for opposed-piston engines

Abstract

A combustion chamber for an opposed-piston engine has an elongated asymmetrical shape in longitudinal section that runs along a chamber centerline, between diametrically-opposed openings of the combustion chamber through which fuel is injected. The asymmetry apportions combustion chamber volume to provide additional clearance on a side of the chamber centerline toward which swirl is directed, thereby giving a fuel plume space to swing without hindrance in response to swirl.

The invention claimed is: 
     
       1. An opposed-piston engine including at least one cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, in which:
 each piston has a crown with an end surface defining a combustion chamber in the cylinder bore with the end face of the other piston when the pistons are near top center locations in the bore; and, 
 the combustion chamber has an asymmetrical shape with respect to a chamber centerline that extends between diametrically opposing openings of the combustion chamber through which fuel is injected; wherein, 
 the asymmetrical shape includes a maximum distance R 1  from the chamber centerline to one side of the combustion chamber; 
 R 1  is positioned a distance L along the chamber centerline on either side of a midpoint of the centerline; and, 
 the asymmetrical shape is polar symmetric with respect to the midpoint of the centerline and provides clearance on a side of the combustion chamber centerline toward which swirl is directed, thereby giving a fuel plume space to entrain air in the presence of swirl, accommodating both fuel plume spreading and fuel plume movement in response to swirl. 
 
     
     
       2. The opposed-piston engine of  claim 1 , in which the cylinder includes a pair of diametrically opposed fuel injector ports with which the opposed openings of the combustion chamber align when the pistons are near the respective top center locations. 
     
     
       3. The opposed-piston engine of  claim 2 , in which the opposing openings provide a sightline between the fuel injector ports that extends without obstruction through the combustion chamber. 
     
     
       4. The opposed-piston engine of  claim 3 , further including a fuel injector with a multi-hole nozzle mounted in each of the fuel injector ports. 
     
     
       5. The opposed-piston engine of  claim 1 , in which the combustion chamber is defined between a bowl in the end surface of a first piston of the pair of pistons and inner walls of ridges that protrude from the end surface of a second piston of the pair of pistons, further in which the combustion chamber's asymmetrical shape is polar symmetric with respect to the centerline midpoint in a reference plane that is transverse to the longitudinal axis of the at least one cylinder and that bisects the combustion chamber. 
     
     
       6. The opposed-piston engine of  claim 5 , in which the cylinder includes a pair of diametrically opposed fuel injector ports with which the opposed openings of the combustion chamber align when the pistons are near the respective top center locations. 
     
     
       7. The opposed-piston engine of  claim 6 , in which the opposing openings provide a sightline between the fuel injector ports that extends without obstruction through the combustion chamber. 
     
     
       8. The opposed-piston engine of  claim 7 , further including a fuel injector with a multi-hole nozzle mounted in each of the fuel injector ports. 
     
     
       9. An opposed-piston engine including at least one cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, in which:
 each piston has a crown with an end surface defining a combustion chamber in the cylinder bore with the end face of the other piston when the pistons are near top center locations in the bore; and, 
 the combustion chamber has an asymmetrical shape with respect to a chamber centerline that extends between diametrically opposing openings of the combustion chamber through which fuel is injected; wherein, 
 the asymmetrical shape includes a maximum distance R 1  from the chamber centerline to one side of the combustion chamber; 
 R 1  is positioned a distance L along the chamber centerline on either side of a midpoint of the centerline; 
 the asymmetrical shape is polar symmetric with respect to the midpoint of the centerline; and 
 the combustion chamber is defined between a first piston end surface on a first piston of the pair of pistons, the first piston end surface including a ridge having an inner wall that transitions to an elongate bowl and a second piston end surface on a second piston of the pair of pistons, the second piston end surface including a ridge having an inner wall that transitions to an elongate bowl. 
 
     
     
       10. The opposed-piston engine of  claim 9 , in which the cylinder includes a pair of diametrically opposed fuel injector ports with which the opposed openings of the combustion chamber align when the pistons are near the respective top center locations. 
     
     
       11. The opposed-piston engine of  claim 10 , in which the opposing openings provide a sightline between the fuel injector ports that extends without obstruction through the combustion chamber. 
     
     
       12. The opposed-piston engine of  claim 11 , further including a fuel injector with a multi-hole nozzle mounted in each of the fuel injector ports. 
     
     
       13. A two-stroke, direct injection, opposed-piston engine including a cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, in which each piston has a crown with an end surface and a sidewall, the end surface and sidewall meeting at a circular peripheral edge centered on an axis of the piston, and the end surface defining a combustion chamber in the cylinder bore with the end face of the other piston when the pistons are near top center locations in the bore; wherein,
 the combustion chamber has an asymmetrical shape defined between first and second end surface ridges positioned on either side of a chamber centerline that extends between diametrically opposing points of the bore; 
 the asymmetrical shape includes a maximum distance R 1  from the chamber centerline to one side of the combustion chamber; 
 R 1  is positioned a distance L along the chamber centerline on either side of a centerline midpoint; and, 
 the asymmetrical shape has polar symmetry with respect to a point on a longitudinal axis of the bore in a plane that is transversal to the longitudinal axis and that bisects the combustion chamber and provides clearance on a side of the chamber centerline toward which swirl is directed, thereby giving a fuel plume space to entrain air in the presence of swirl, accommodating both fuel plume spreading and fuel plume movement in response to swirl. 
 
     
     
       14. The two-stroke, direct injection, opposed-piston engine of  claim 13 , in which the combustion chamber is defined between a bowl in the end surface of a first piston of the pair of pistons and inner walls of ridges that protrude from the end surface of a second piston of the pair of pistons. 
     
     
       15. A two-stroke, direct injection, opposed-piston engine including a cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, in which each piston has a crown with an end surface and a sidewall, the end surface and sidewall meeting at a circular peripheral edge centered on an axis of the piston, and the end surface defining a combustion chamber in the cylinder bore with the end face of the other piston when the pistons are near top center locations in the bore; wherein,
 the combustion chamber has an asymmetrical shape defined between first and second end surface ridges positioned on either side of a chamber centerline that extends between diametrically opposing points of the bore; 
 the asymmetrical shape includes a maximum distance R 1  from the chamber centerline to one side of the combustion chamber; 
 R 1  is positioned a distance L along the chamber centerline on either side of a centerline midpoint; 
 the asymmetrical shape has polar symmetry with respect to a point on a longitudinal axis of the bore in a plane that is transversal to the longitudinal axis and that bisects the combustion chamber; and 
 the combustion chamber is defined between a first piston end surface on a first piston of the pair of pistons, the first piston end surface including a ridge having an inner wall that transitions to an elongate bowl and a second piston end surface on a second piston of the pair of pistons, the second piston end surface including a ridge having an inner wall that transitions to an elongate bowl. 
 
     
     
       16. A piston for an opposed-piston engine, the piston including a longitudinal axis and comprising:
 an end surface having a shape that defines a combustion chamber with the end surface of an opposing piston in a cylinder bore of the opposed-piston engine; 
 a circular sidewall centered on the piston's longitudinal axis and extending from the end surface; 
 a circular peripheral edge where the sidewall meets the end surface; 
 notches in the peripheral edge at respective ends of a diameter of the peripheral edge, through which fuel is injected into the combustion chamber; and, 
 the shape of the end surface includes at least one elongated ridge that extends between the notches and projects through a reference plane that is transverse to the longitudinal axis and contains the peripheral edge; 
 the at least one elongated ridge including an outer wall that faces the peripheral edge and an inner wall that faces the diameter; 
 in which the combustion chamber formed by the inner wall of the at least one elongated ridge has an asymmetric cross-section in the plane of reference with respect to the diameter of the periphery; and, 
 in which a curvature of the inner wall in the plane of reference is polar-symmetric with a curvature of an inner wall of an opposing ridge with respect to a midpoint of the diameter. 
 
     
     
       17. The piston for an opposed-piston engine of  claim 16 , in which the shape includes two ridges having inner walls that transition to a cleft between the ridges that extends between the notches. 
     
     
       18. The piston for an opposed-piston engine of  claim 16 , in which the shape includes only one ridge and the shape is identical to the end surface shape of the opposing piston. 
     
     
       19. A method for operating an opposed-piston engine including a cylinder, a pair of opposed pistons in the bore of the cylinder and spaced-apart intake and exhaust ports controlled by the pistons, by:
 introducing swirling charge air into the cylinder between end surfaces of the pistons; 
 moving the pistons toward each other in a compression stroke; 
 forming a combustion chamber between the end surfaces of the pistons, the combustion chamber having an asymmetrical shape with respect to a chamber centerline that extends between diametrically opposing openings of the combustion chamber, wherein:
 the asymmetrical shape includes a maximum distance R 1  from the chamber centerline to one side of the combustion chamber, 
 R 1  is positioned a distance L along the chamber centerline on either side of a midpoint of the centerline, and 
 the asymmetrical shape is polar symmetric with respect to the midpoint of the centerline and provides clearance on a side of the combustion chamber centerline toward which swirl is directed, thereby giving a fuel plume space to entrain air in the presence of swirl, accommodating both fuel plume spreading and fuel plume movement in response to swirl; and, 
 
 injecting opposing spray patterns of fuel into swirling charge air in the combustion chamber through the opposing openings. 
 
     
     
       20. The method of  claim 19 , wherein each of the spray patterns has three plumes. 
     
     
       21. The method of  claim 19 , wherein each of the spray patterns has four plumes.